Ric Flair believes the WWE is ripping him off -- using the phrase The Man without his permission ... and now he's threatening legal action.
Flair says he's been referring to himself as The Man since 1981 -- and even holds the trademark for his famous catchphrase, "To be the man, you gotta beat the man."
The problem ... one of WWE's biggest stars -- Becky Lynch -- has been referring to herself as The Man over the past year and the nickname has become a huge hit with fans.